A major aim of our studies is to understand in chemical terms the differences between neurons that underly their physiological function. Our initial efforts have concentrated on the identification of synaptic transmitter compounds and learning something of the reasons for their accumulation within neurons. Our approach is to bring together physiological and anatomical techniques with micro-biochemical studies in a multi-discipline study. A simple nervous system (the lobster nervous system) was selected for these studies because of its favorable anatomy. Neurons are large, relatively few in number (compared to vertebrates) and axons and cell bodies of single physiologically identified nerve cells can be isolated repeatedly from a series of animals. This allows one to carry our detailed chemical and physiological analyses on single types of functionally identified neurons. A more recent interest in our laboratory is in how synaptic contacts can be modulated, i.e., made to work more or less efficiently for finite periods of time. With the present application we hope to develop systems to study this phenomenon in some detail. Our past studies have been concerned with gamma-aminobutyric acid, the inhibitory transmitter compound at lobster neuromuscular junctions, glutamic acid, the leading candidate for the excitatory transmitter at the same junctions, and acetylcholine, the probable lobster sensory transmitter compound. In this application we concentrate on octopamine, the phenolamine analogue of norepinephrine. Octopamine may function as a lobster neurosecretory substance.